<!DOCTYPE html>
<html>
<head>
  <style type="text/css" media="screen">

    body {
      background-color: silver;
      padding: 10px;
    }

   .container {
     position: absolute;
     height: 100px;
     width: 100px;
     margin: 10px;
     left: 0;
     top: 0;
     z-index: -1;
     background-color: blue;
   }

   .compositing {
     will-change: transform;
   }
  </style>
</head>

<body>

  <!-- the body background should cover the entire viewport. No red should be visible in debug builds. -->
  <div class="container">
    <div class="compositing">
      Compositing
    </div>
  </div>

</body>
</html>